Method of treating cutting tools



each other. cutting edges form four wings or flights spaced two wings.

Patented Mar. 24, 1942 UNITED STATES PATENT OFFICE- METHOD OF TREATING CUTTING TOOLS Jean La Force, San Francisco, Calif.-, and Arthur K. Seemann, Garden City, N. Y., assignors to The Linde Air Products Company, a' corporation of Ohio No Drawing. Application July 11, 1940, Serial No. 344,915

6 Claims.

' having at one end thereof an integral bit formed by forging or upsettingthe metal at the end of the rod. A hole running centrally through the rod supplies water to wash away the products of drilling and preclude the presence of dust in the air. There are many different types of bits formed on the ends of drill steel, but each type includes one or more cutting edges extending transversely of the end of the drill, the most prevalent being the cross or X type in which two transverse cutting edges are perpendicular to In this type, the two transverse 90 apart, and what may be termed cutting surfaces slope downwardly and inwardly on either side of each cutting edge to a valley between each wing. The periphery of the bit flares outwardly, forming a gauge cutting or reaming edge at the outer corner of each wing. An older type, known as a fbull bit and used mostly in hand rather than machine drilling, has only one transverse cutting edge forming two wings, but also fiares outwardly at the corners of the There are also two types of bits from the standpoint of the discharge of waterend-ho1e minate at the side i.-e. inthe valley or valleys between the wings.

The end of the drill steel opposite the bit may be inserted in a hammer or similar machine, which is usually operated by compressed air and which imparts successive impacts to the drill, at the same time turning the drill as drilling progresses. As soon as the reaming edges, or the reaming and cutting edges, become dull, the

edges remain out to gauge. However, when the reamingedges become rounded ofi, the drill sticks in the hole.

The resharpening of drill steel is normally accomplished by a hot forging operation, succeeded by suitable heat treatment to produce a fine grained structure and to harden the bit end of the drill. However, drill steel-ranges in length from 2 up to or more feet, and the transportation of drill steel to and from a forge shop consequently involves considerable expense. The use of bits formed integrally on drill steel also requires an excessive number of drills, involving a considerable tonnage of steel, most of which lies idle a greater part of the time. By the use of detachable bits, a considerably smaller tonnage of steel is involved in any mining or construction operation, and such detachable bits are easily transported and handled in large quantities. Detachable bits. normally have at one end the cutting and reaming edges and at the other end an internally threaded skirt, being only a few inches in length. Detachable bits are secured to a shank provided with threads at one end, and the shanks, which may vary from 2 to 20 feet or more in length remain at the scene of operation. Thus, it is necessary to transport only the detachable bits to and from a forge or other shop where they are to be resharpened. About 95% of the detachable bits now in use in this country are of the Xor cross type.

drill must be resharpened. The transverse cutting edges may be quite worn but the drill will still operate satisfactorily as long as the reaming When detachable bits were first used, it was thought that each bit could be used until worn, and then discarded. However, it was found to be more economical to resharpen worn ordull bits, and various ways of carrying this out were developed. In a practice now largely used in resharpening detachable bits of the X or cross type and formed of steel having approximately 1.10% C., the bits are heated in a continuous or batch furnace to about 1800 F., the heating period being about 25 minutes. After removal from the furnace, each bit is placed on a milling arbor and then brought to a milling machine at which milling cutters, partially by hot milling and partially by forging or upsetting, reshape the bit to form new cutting edges and new reaming edges. Due to the temperature to which each bit is heated and also the amount of time spent in the heating furnace, a considerable grain growth in the steel forming the bit takes place. It is therefore the practice to permit each bit to anneal or cool slowly in air after hot milling, reheat to a temperature of about 1425 F., and then quench to harden the cutting and reaming edges and produce a finer grain structure. A special quenching device is used, the cutting and reaming edges only being hardened by immersion of the cutting'end of the bit to a predetermined depth in a water bath. After this selective quenching, which of course does not improve the properties of the skirt and threads, the bits are partially stress relieved in boiling water for two hours or more.

Another disadvantage of the furnace heating method is the decarburization and oxidation of the steel forming the bit. drill bits are heated in ordinary furnaces, scaling is produced by the presence of a large amount of air in the furnace. This may be prevented to some extent by careful operation of the furnace or by heating in an atmosphere substantially free from oxygen, both of which solutions involve considerable added expense. A limited amount of oxygen in the furnace atmosphere will combine with the carbon in the surface of the steel to decarburize the surface. Continuation of the heating will produce oxidation and scaling of the surface. Either condition is undesirable, as decarburized steel has lost strength and scaling is objectionable as such scale on the threads of the bit tends to cause jamming or freezing of the bit to the drill shank when in use.

Among the objects of this invention are to provide a method of treating a cutting tool having one or more cutting edges wherein new cutting edges may be formed without causing excessive grain growth in any part of the tool; to provide such a method wherein the heating time is a matter of only a few seconds; to provide amethod of resharpening a drill bit wherein onlythe surfaces at the cutting end of the bit are heated to a reshaping or hot milling temperature; to provide such a method in which grain growth in the cutting edges is minimized and the formation of scale on the threads is avoided; and to provide such a method in which the cutting When drill steel or I to be given a special heat treatment prior to' hardening the cutting edges.

The method of this invention may be used in treating any type of tool having one or more cutting edges, and may be used in resharpening drill steel having integral bits, either end-hole or side-hole, formed thereon. However, the method of this invention is particularly useful in the resharpening of detachable drill bits, in which the ease and economy of treatment and value of results secured are particularly outstanding.

In practicing the invention as applied to the treatment of a drill bit, the surfaces at the cutting end of a conventional cross or X type of detachable bit, i. e. the cutting edges, cutting surfaces, valleys, and reaming edges, may be quickly heated to the proper temperature by a blowpipe flame manipulated by the operator, but the difll culties involved in heating manuallyso that all portions of the surface of the cutting end of the bit reach the proper temperature at the same time make it desirable, in order to achieve the best results, to use a multi-flame blowpipe head and reaming edges may be quenched immediately after reshaping to harden the same. Other objects and the novel features of this invention will become apparent from the following description.

Worn or dull cutting tools are treated in accordance with this invention by locally heating only those surfaces which are to be reshaped in order to form new cutting edges; and after reshaping, the heated portion of the tool is cooled at a sufficiently rapid rate to harden the same.

The surfaces to be reshaped are preferably heatedto a slight depth by one or more high temperature heating flames, such as provided by a come bus'tible mixture of oxygen and acetylene, but

other sources of localized high temperature heat,

such as an electric arc or an electric induction operation, so that the quenching or rapid cooling operation, which preferably follows substantially immediately after the reshaping operation, will cause the cutting edges to be hardened. Since only the cutting edges and surfaces closely adjacent thereto are heated to any appreciable extent, the rest of the tool will remain in a desired and automatic or semi-automatic apparatus. The bit to be resharpened may be mounted on a spindle which is pivotally mounted on a horizontally movable carriage or a turntable. In one position, the bit is disposed in front of, underneath, or above a multi-fiaine blowpipe adapted to direct a plurality of heating flames against the surfaces to be heated. It is'preferred to position the'bit above the blowpipe head during heating, because the natural flow of gases upwardly as sists in effectively heating the valleys between the wings. A multi-flame blowpipe having a plurality of removable tips may be used, in case there is a considerable difference in the sizes of bits to be treated, since outlets not in use can be plugged.

The bit may be rotated on the spindle during heating, in which case no part of the blowpipe head or tips can extend further toward the bit than the cutting edges. When the bit is positioned above the blowpipe head, the bit may remain stationary during heating, and a head used in which the ends of the tips substantially conform to the shape of the cutting end of the bit. When a large number of bits of the same size are to be treated, a head having outlets drilled in the face thereof rather than removable tips, may be used. Such a head also may conform in shape to the cutting end of the bit. It is also desirable to space the outlets or tips more closely together adjacent the center'of the bit and along the sides of the valleys, and'at greater distances apart along the cutting edges, to compensate for the tendency for a lesser amount of heat to be conducted away from the cutting edges.

As soon as the surfaces at the cutting end of the bit have reached the proper temperature, at the end of a heating period of, say, 30 seconds, the carriage or turntable is moved to place the bit in a second position, opposite'a suitably shaped milling cutter. In the case of cross or X types of 2,277,117 Y bits, each valley is in turn pressed against the wear evenly around the sides and a considerably greater amount of'drillingcan be done before the reaming edges become rounded over sufcause a plastic flow of the heated surface metal takes place. of the surface metal as possible, in order to permit a large number of resharpenings.) Instead of a milling cutter, a smooth surfaced wheel may be used, the bit being forced against the same with sufiicient force to produce the desired reshaping.

After the valleys have been reshaped, which produces new cutting edges, the bit on the spindle is rotated to a position alongside the milling cutter, in order to reshape the outer periphery of the bit and produce new reaming edges. Hot milling tends to raise the temperature of the cutting edges, and' later of the reaming edges, so that the reaming edges will be above the critical temperature at the end of the reshaping operation. Furthermore, the entire reshaping operation, with proper equipment, need take no more than about seconds, and there is thus substantially. no opportunity during shaping of the (It is desirable to remove as little reaming edges for the cutting edges to cool bequenching medium, and thereby harden the cut- Since only the cutting ting and reaming edges. end of the bit has been heated, the entire bit may be immersed in the quenching medium without affecting the skirt and threads. In case the new cutting and reaming edges have been produced by a reshaping operation which, unlike hot milling, may leave the edges at a temperature lower than the critical, these edges may easily be reheated to a temperature above the lower critical by the same heating head by which they were heated prior to the reshaping opeartion. In any event, the amount of reheating necessary will be relatively small.

If desired, a stress-relieving draw from a suitable temperature, preferably about 400 F., may be given to the treated bit after the cutting and reaming edges have been'hardened. Preferably, this is a self -drawing operation, accomplished by removing the bit from the quenching bath as soon as the cutting edges have reached the draw- 1 ing temperature and then'cooling the bit slowly in an.

The advantages of the foregoing treatment are that the skirt" and threads are not heated to any appreciable extent, and there is thus no opportunity for grain growth, decarburization, or the formation of scale; the heating time, by utilizing a source of localized high temperature heat, is normally a matter of only a fraction of a minute, so that grain growth in the cutting and reaming edges is held to a minimum; the time consumed in treating each bit is only a fraction of that consumed in furnace treatment; and each bit is quenched substantially immediately after reshaping, thus omitting a heating step which has previously been thought to be necessary. In addition, the resulting bit is more satisfactory than bits resharpened by prior methods, because the reaming edges have been found to be selfsharpening during use, i. e., the learning edges ficiently to cause the bit to stick in the hole.

Although the treatment of the cross or X type of detachable drill bits has been described in detail, it will be-appreciated that other types of drill bits or other cutting tools may be treated with equal success. For instance, a type of detachable bit recently introduced, which may be termed a W type of bit, has only one transverse cutting edge, forming two wings 180 apart and is provided with 'a 'pair of oppositely disposed wings each spaced 90 from the cutting wings.

Each of the latter wings is provided with a reaming edge extending about peripherally around the cutting end of the bit, and the two wings thus provide about 90 of reaming edge. The top of this bit, viewed from the end of a cutting wing, appears as a flattened letter W, and'an advantage claimed therefor is that only a single pass across a W-shaped milling cutter is. needed to reshape the top of the bit, instead of the four or eight passes used in reshaping the top of a cross or X type of bit. Although a differently shaped heating head and a differently shaped milling cutter must be used, the resharpening of the W type of bit in accordance with this invention involves substantially the same toperations as-just described in connection with the cross or X type of bit.

From the foregoing, it will be seen that the method of this invention provides a speedy, facile, and highly satisfactory method of resharpening detachable drillv bits, as well as treating other types of cutting tools to provide new cutting edges, particularly when the old cutting edges have become Worn or dull. It will be understood that various changes in the method of this invention may be made without departing from the spirit and scope thereof, as defined in the appended claims.

What is claimed is:

l. A method of treating a quench-hardenable cutting tool having at least one cutting edge, which comprises locally heating the surfaces of said tool adjacent each cutting edge; reforming and shaping the cutting end of said tool to prorock drill bits which comprises locally heating.

vide new cutting edges; and substantially immediately thereafter cooling at least each new cutting edge from the critlcal'temperature at a sufficiently rapid rate to harden the same.

2. A method of sharpening quench-hardenable the surfaces at the cutting end of a bit; reforming and shaping the cutting end of said bit to provide new cutting and reaming edges; and substantially immediately thereafter cooling at Y least the new cutting and reaming edges from the critical temperature at a sufliciently rapid such surfaces to a temperature substantially at or above the critical range; reforming and shaping the cutting end of said'bit to provide new cutting and reaming edges; and substantially immediately thereafter, and before said new cutting and reaming edges have cooled to a temperature below the critical range, subjecting at least the new cutting and reaming edges of said bit to a cooling medium so as to harden the same.

5. A method of sharpening quench-hardenable rock drill bits which comprises positioning a bit with the cutting end thereof extending downwardly; applying a plurality of high temperature heating flames to the surfaces at the cutting end a of said bit, said heating flames being directed upwardly against said surfaces so that hot gases will flow upwardly through the valleys between the wings of said bit; after said surfaces have been heated, reforming and shaping the cutting end of said bit to provide new cutting and reaming edges; and thereafter cooling at least said new cutting and reaming edges from the critical temperature at a suiliciently rapid rate to harden the same.

6. A method of sharpening quench-hardenable rock drill bits which comprises locally heating 

